1. Field of the Invention
This invention relates to card reading devices and the like for use in electronic data processing and, more particularly, to photo-electric data reading arrangements and signal generating circuitry useful in combination therewith, for card reading apparatus adapted to read information in the form of punched holes, marks, and both holes and marks.
2. Description of the Prior Art
Prior art card readers have for some time now utilized highly efficient light sources such as LEDs in combination with photosensitive components such as phototransistors, for the detection of information encoded onto paper cards, i.e., punched holes and marks. Techniques for utilizing such efficient components in a highly efficient and reliable form have been worked out and incorporated widely into card readers and other forms of optical reading equipment used in the data processing industry. However, due to the nature of the difference between the manner in which cards are encoded with hole and mark information respectively, generally card reading devices are designed as either punched hole readers, or mark sense readers.
In order to enhance the adaptability, and accordingly the usefulness, of card readers, the industry has called for card reader models which are designed with a capability of reading either type of encoded information. As a general proposition, such plural-mode card readers generally incorporate a combination of the sensing and detection arrangements as are used separately in standard hole and mark type readers respectively. The utilization of a single, as opposed to plural, sensing arrangement for the detection of either holes or marks is clearly a desirable design achievement in the card reader industry. However, the nature of the optical signals conventionally generated for the two different modes of encoded data has not heretofore permitted a completely satisfactory solution, e.g., a design which approaches the ideal of having a single read circuit of the same simplicity and reliability as used in either a prior art punched hole reader or a prior art mark sense reader.
In addition to the hole sensing mode and mark sensing mode of operation, there is a need for a card reader which is adapted to simultaneously read both hole and mark information. In many situations, cards may be first processed such that information is encoded in a limited number of columns in a first manner, e.g., punched holes, and at some later time information is encoded in other columns in a second manner, e.g., marks. For whatever reasons the user may have for encoding the information in one mode or the other, or both, it is highly desirable to have the card reader incorporate the capability of sensing and accurately reading any one of the three modes, which capability is embodied in an efficient and reliable manner.